This research proposal is concerned with the study of the fusion process used by the human parainfluenza 3 virus (PF3), one of the major etiological agents responsible for lower respiratory tract illness in children. Because of the primary importance of membrane fusion in the replication of Paramyxoviridae, these viruses provide a good model for studying the molecular basis of this process. The PF3 contains two surface glycoproteins, HN, which has hemagglutinating and neuraminidase activity, and F, which has fusion activity. Although these proteins have discrete biological activities, there is a growing body of information that a more intimate interaction between the two proteins is necessary for viral-mediated membrane fusion. The specific aims of this proposal are to (1) select viral F and HN glycoprotein variants by using analogs and monoclonal antibodies which are inhibitory to neuraminidase and fusion activity, and (2) the expression and co- expression of recombinant glycoprotein genes for the purpose of performing site specific mutagenesis studies. The first aim is to be studied using traditional virological methods and is the first step in generating glycoprotein variants. The second aim will require the utilization of recombinant DNA techniques for the generation and analysis of variant glycoproteins. This proposal is unique from other paramyxoviral studies in that we plan to examine the interaction of both F and HN in the fusion process using a virus which causes significant respiratory disease in humans. In addition, the utilization of an expression vector system to generate a number of variant proteins which diverge in amino acid sequence at a specific position also makes this study unique. The long-term goal of this research is to develop an understanding of the molecular mechanism of viral mediated membrane fusion for the purpose of interferring with this process. This goal may have some practical application in the prevention or amelioration of a number of virus induced respiratory diseases.